1. Field of the Invention
The present invention relates generally to honeycomb structures, and more particularly, to shaped honeycomb structures and the method and apparatus for making the shaped honeycomb structures.
2. Description of the Related Art
Honeycomb core or paper honeycomb structure is a three-dimensional lattice formed by a plurality of abutting partition walls. The partition walls are arranged in a generally oval or hexagonal honeycomb pattern to form hexagonal cells. The hexagonal cells have opposed bottom and top hollow-cell hexagonal faces on opposite sides of the core respectively.
Typically, honeycomb core is constructed from unbleached kraft paper; however, other types of paper or paperboard, including recycled fibers, may be used. Additionally, the hollow-cells of the core can be resin-impregnated for water resistance. Other materials, such as plastic film can be used on the cells if desired. The width of the cells, the height of the partition walls, and the weight of the kraft paper can all be varied to impart various characteristics to the honeycomb core as well known to one of ordinary skill in the art.
Conventional honeycomb structures, typically called honeycomb panels, have generally perpendicular partition walls and a general hexagonal cell pattern rigidly fixed in place by a cured resin such as phenolic formaldehyde as known to one of ordinary skill in the art. The typical honeycomb panel further includes the rigid honeycomb core sandwiched between a top face sheet and a bottom face sheet. The top and bottom face sheets respectively are abutted against and adhesively secured to the top and bottom hollow-cell faces of the honeycomb core, respectively. The top and bottom face sheets may be made of a kraft paper; however, other materials such as metal foil and plastic sheet may be used.
Conventional honeycomb structures exhibit high compression and impact strength. Because of the honeycomb panels"" high strength and durability combined with their light weight, honeycomb panels have many uses, such as protective packaging and as structural cores. For example, honeycomb panels may be used in module office furniture dividers. Additionally, honeycomb panels may be used as corner or edge protectors in the packaging industry.
Often to use honeycomb panels as structural cores or as protective packaging, the honeycomb panel must be folded into a desired shape. For example, a simple edge is protector consists of a honeycomb panel folded into two portions to conform to the two intersecting surfaces of the corner. To fold the honeycomb panel, the panel is typically pressure scored, slit scored, V-cut scored or angle crush slit scored.
A pressure score is typically formed by pressing a cylinder into the honeycomb panel forming an arced depression. The arced depression of the pressure score provides a hinge about which the honeycomb panel may be folded. One shortcoming of shaping the honeycomb panel using the pressure score is that the pressure-scored panel often does not fold predictably along the chosen line. Additionally, the pressure-scored panel is difficult to fold and readily returns to its flat position. Furthermore, the pressure score lowers the compression and impact strength at the fold.
A slit score is typically formed by a knife cutting completely through the top face sheet and the honeycomb core, leaving only the bottom face sheet intact to act as a hinge. The panel is then folded away from the slit. One shortcoming of shaping the honeycomb panel using the slit score is the corner impact strength is low because only the second face sheet protects the corner.
A V-cut score is typically formed by sawing a V-shaped trough through the top face sheet and into the honeycomb core with the vertex of the V being just above the second face sheet. The panel is then folded about the V-shaped trough. One short coming of the V-cut score is the complexity of equipment needed to cut and remove V-shaped trough. Additionally, the V-cut panel readily returns to its flat position after being folded unless an adhesive is applied to hold the panel in the folded position.
An angle crush slit score is typically formed by slitting the top face sheet and driving a wedge into the honeycomb core to crush the core to a predetermined depth at a predetermined angle. The panel is then folded about the angle crush slit score. The angle crush slit score is described in U.S. Pat. No. 5,466,211 entitled xe2x80x9cMethod and Apparatus for Manufacturing Articles Employing Folded Honeycomb Panels.xe2x80x9d One shortcoming of the angle crush slit score panel is that it readily returns to its flat position after being folded unless an adhesive is applied to maintain the panel in the folded position.
Thus, a need has arisen for shaped honeycomb structures which will provide a structurally sound honeycomb core, which will provide high compression and impact strength and which will retain the desired shape and for a method and apparatus for forming the shaped honeycomb structures.
In accordance with one aspect of the present invention, there is provided a shaped honeycomb structure comprising a honeycomb panel having a plurality of abutting partition walls forming a plurality of abutting cells defining a plurality of abutting top and bottom hollow cell faces respectively. The shaped honeycomb structure also includes a permanently fixed fold in the panel defining a first panel portion and a second panel portion. The first panel portion converges at an angle with the second panel portion at the fold. The partition walls of the fold are not vertically deformed. At the fold, the top hollow cell faces are laterally compressed, and the bottom hollow cell faces are laterally expanded. The shaped honeycomb structure may further include a top face sheet adhered to the top hollow cell faces and/or a bottom face sheet adhered to the bottom hollow cell faces.
In accordance with another aspect of the present invention, there is provided a method of forming a shaped honeycomb structure comprising expanding an unexpanded honeycomb core comprising a plurality of strips of material adhered together to form an expanded honeycomb core comprising a plurality of abutting partition walls forming a plurality of cells defining a plurality of abutting hollow cell faces on a top side and a bottom side of the expanded honeycomb core. The expanded honeycomb core is impregnated with a resin. The method further comprises forming a fold portion in the expanded honeycomb core. In the fold portion, the partition walls are not vertically deformed, the top hollow cell faces are laterally compressed and the bottom hollow cell faces are laterally expanded. The method further includes completely curing the resin of the honeycomb core with the fold portion to permanently rigidly fix the plurality of abutting partition walls into the plurality of abutting hollow cell faces with the fold portion. The method may further include a step of partially curing the resin of the expanded honeycomb core to generally flexibly fix the plurality of abutting partition walls into the plurality of abutting hollow cell faces. Additionally, the method may further comprise a step of adhering a top face sheet to the top hollow cell faces and/or adhering a bottom face sheet to the bottom hollow cell faces with said top hollow cell faces of the honeycomb core having said fold portion.
In accordance with a further aspect of the present invention, there is provided an apparatus for forming a shaped honeycomb structure comprising a fold portion. The apparatus comprises an expanding station capable of expanding an unexpanded honeycomb core comprising a plurality of strips of material glued together to form an expanded honeycomb core comprising a plurality of abutting partition walls forming a plurality of cells defining a plurality of abutting hollow cell faces on a top side and a bottom side of the expanded honeycomb core. The expanded honeycomb core being impregnated with a resin. The apparatus also includes a forming station capable of placing a fold in the expanded honeycomb core. At the fold, the partition walls are not vertically deformed, the top hollow cell faces are laterally compressed and the bottom hollow cell faces are laterally expanded. The forming station is further capable of completely curing the resin of the honeycomb core with the fold to permanently fix the plurality of abutting partition walls into the plurality of abutting hollow cell faces with the fold. The apparatus may further include a partial curing station capable of partially curing the resin of the impregnated expanded honeycomb core to generally flexibly fix the plurality of abutting partition walls into the plurality of abutting hollow cell faces. The apparatus may further include a gluing station capable of applying an adhesive to the top hollow cell faces to adhere a top face sheet to the top hollow cell faces.